To observe the limiting values of the exhaust gas in internal combustion engines, exhaust gas treatment systems are used which contain a catalytic converter, a particle filter or other components suitable for exhaust gas treatment, for example. The components used often operate in an optimum manner only in a certain temperature range. If the components have storage properties regarding at least one exhaust gas component, the laden state by the exhaust gas component must be monitored.
To detect the temperature as a measured quantity, temperature sensors are used, which may be situated in the intake area, on the internal combustion engine itself, or in the exhaust area. To detect pressure as a measured quantity, pressure sensors are used, which may be used to determine the laden state of a particle filter, for example. The pressure sensors detect the pressure difference occurring at the particle filter, which is a measure of the laden state. Additional pressure sensors may be situated in the intake area of the internal combustion engine.
If a sensor delivers an erroneous signal, this may result in erroneous control of the internal combustion engine and of the exhaust gas treatment system. The consequences include increased fuel consumption of the internal combustion engine and increased exhaust gas emissions.
Proper operation of the overall system is ensured only if the sensors used deliver a reliable sensor signal. German patent document no. 101 12 139 discusses a method for monitoring sensors which detect a measured quantity of an internal combustion engine. These may include temperature sensors, pressure sensors or other sensors. The individual sensor signals are compared to a reference signal delivered by an additional sensor, which is not involved in the diagnosis itself.
The sensor which is not involved in the diagnosis is situated at a point where there is a relatively light load on the sensors such as the intake area in which a temperature sensor is exposed to less temperature fluctuations than it would be in the exhaust area. Defective sensors are detected by forming the difference between the individual sensor signals of the sensors to be monitored and the reference signal of the non-monitored sensor and comparing it to the predefined threshold values. If no error is recognized in the preceding procedure steps, a plausibility check is finally performed by forming the differences between the signals of the sensors being monitored and comparing them to threshold values.